While trying to make a walk/run animation CTRL+SHIFT+V doesn't work correctly
The symmetry of the IK controllers is bad, here is what we have currently:

If I delete the right leg and symmetrize the left leg, here is what I have:

Now it works correctly, except I'm not sure about your feet Copy Rotation constraint but it's another problem... (I would rather parent the feet to the controllers and give them a Copy Location with the lower legs as targets and the Head/Tail value at 1).